Window coverings such as curtains, draperies, shades and blinds have been widely used in households and office environments. The extension or retraction of the curtains mostly are done through pulling cords. This type of operation generally is adapted for Venetian blinds or curtains composed of a left and a right panel, but is not adaptable to one-piece curtain. Applicant has disclosed a curtain apparatus which includes an actuating means located on the left end of the track. Pulling the actuating means once, the curtain will be extended clockwise downward. Pulling one more time, the curtain will be retracted counterclockwise upward. When the curtain is retracted, a buffer apparatus located on the right end of the track will be wound slowly. However, when the curtain is retracted, the friction coefficient of the buffer apparatus is relatively large and will generate noise.